This invention relates to an improvement in contact lenses and intraocular lenses possessing phase plate optics. A "phase plate", as employed herein and in the claims, is a unitary optical region of a lens utilizing the combination of a zone plate and optical facets in the zones said combination diffracts light to produce a specific wavefront which results in a specific intensity distribution of light at the various order (e.g., 0.sup.th, 1.sup.st, etc.) foci of the zone plate.
This invention concerns contact lenses, and more particularly contact lenses utilizing phase plate optics, such as phase plate bifocals and "tuned" Fresnel lenses making use of concentric annular zones. Such lenses generally follow the designs described, for example, by Allen L. Cohen in U.S. Pat. Nos. 4,210,391; 4,338,005; and 4,340,283. The lens design of Cohen, supra, provides that the radii "r" of the annular and concentric zones are substantially proportional to .sqroot.n and that the zones are cut so as to direct light to more than one focal point (herein called a "Cohen lens design").
The Cohen lens design with phase plate optics allows lens constructions which are exceptionally thin. Contact lenses may be designed with phase plate optics in order to achieve a bifocal or multifocal effect. The specific chromatic properties of a phase plate may be incorporated in the design of a contact lens including a contact lens having multifocal properties.
It has been determined that contact lenses with phase plate optics can generate some problems for the wearer. One is the glare that can result from the non-optical edges of the steps between the annularly arranged eshelettes that make up a phase plate and appears through wave interference as a disconcerting, intense light to the contact lens user.
Another potential problem stems from (i) the need in soft contact lenses to have sufficient mobility in the lens' fit to the cornea to allow tear fluid exchange to cleanse the surface of the eye of metabolic waste and (ii) the inability of the soft lens to move sufficiently during wearing to satisfy that needed mobility.
The provision of a multiplicity of multifocal Fresnel eshelettes in the annular zone plate arrangement of the Cohen lens design in a soft contact lens tends to limit the mobility of the lens. It would be desirable to incorporate into the design of such lenses sufficient mobility that the lens has the capacity of moving about 0.5 to about 1 millimeter of distance during wearing. This would enhance the lens' ability to allow management of the buildup of metabolic waste under the lens.
It is the intent of this invention, amongst other things, to provide a multifocal contact lens design encompassed within the annular arrangement of the Cohen patents, supra, which minimizes the effects of glare from the non-optical edges and/or possesses the requisite mobility during use, as characterized above. The invention achieves these results and affects the multifocal utility of a lens with the aforementioned annular arrangement.